ABSTRACT
Ideal ground conditions for EPB machines consist of soils with relatively high fines contents such as clayey silts or silty sands, with a consistency to form a low permeability, soft plastic paste when excavated. These properties allow the support pressure to be transferred uniformly to the tunnel face and controlled flow of the soil through the machine. The compressibility of soil has an important function on machine performance. However, natural soils rarely have these ideal properties, and conditioning of the soil is usually necessary to change its properties to suit the machine. Soil conditioning for EPB machines involves injecting conditioning agents into the excavated soil. The objective is to modify the soil properties to form a soft plastic paste, leading to improvements in the machine performance and control of the excavation process in a wide range of soils. The specific treatments required to effectively condition different types of soil. Many factors influence the specification and performance of soil conditioning treatments.
